One well known technique of fracturing is called “plug and perforate”. In this technique a procedure is repeated in a down-well to up-well direction. The initial perforations are made in the borehole with a perforating gun and those perforations are treated. Thereafter a plug and gun are run in and the plug is set to isolate the already treated perforations. The gun is released and repositioned before being fired and removed from the borehole. Treatment fluid is pumped to initiate fractures in the second interval. This process may be repeated multiple times. After that the plugs are left in place, milled out, allowed to disintegrate, or otherwise modified to permit production through a production casing.
The problem is that each perforated interval has rock formations than can have differential breakdown stress. Under the traditional technique of pumping into the interval after perforating the interval, the entire interval may not be uniformly treated as the weaker rock formations will preferentially admit more flow than the stronger formations in the same interval. Thus, the portion of the interval with the stronger formations will be under-fractured due to the pumped flow taking a path of less resistance through the more easily fractured rock.
The method of the present invention addresses this issue with a plug design that has an integral passage that is initially obstructed with a rupture disc set to break at a predetermined high pressure that is high enough to fracture even the rock with the highest breakdown stress in the interval. The breaking of the breakable member or rupture disc ensures the spike of delivered pressure is high enough to initiate fractures at every cluster in the stage interval. The plug has a ball seat to accept a ball to isolate the just treated interval, and in some executions with a feature that retains the ball to the seat against the potential effect of swabbing out when the gun fired above it is pulled out of the hole. The process repeats in each interval before the plugs are removed. These and other aspects of the present invention will be more readily apparent to those skilled in the art from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined from the appended claims.
Devices that use rupture discs for access to devices or the formation itself are described in U.S. Pat. No. 8,393,392; U.S. 2015/0129218 and WO/2014/035420. U.S. Pat. No. 5,425,424 illustrates the use of multiple rupture discs associated with multiple telescoping assemblies as well as pressure regulation devices with a goal of ensuring that all the telescoping assemblies extend as a way of producing a formation without perforation.